Lubricating composition

ABSTRACT

The present invention provides a lubricating composition, at least comprising: —a base oil; —a metal sulphide or metal oxide, preferably a metal sulphide; and —an organosulphur compound. In a further aspect the present invention provides the use of the above lubricating composition for improving one or more of extreme pressure and anti-wear properties.

The present invention relates to a lubricating composition comprising a metal sulphide or a metal oxide, in particular to a grease.

It is known to use bismuth sulphide (Bi₂S₃) in a grease, as an alternative to molybdenum disulphide (MoS₂). As an example, O. Rohr at al., “Investigation on the Effect of Bismuth Sulfide on Load Carrying Capacity in Greases as a Solid Lubricant”, NLGI Spokesman, Volume 69, Number 12, pages 8-13, March 2006 (presented at NLGI's 71^(st) Annual Meeting in October 2004) suggests to use bismuth sulphide as an extreme pressure additive in a grease.

A problem of the above known grease is that it shows relatively poor load carrying properties as determined with the four-ball test according to ASTM 02596.

It is an object of the present invention to minimize the above problem.

It is another object to provide an alternative lubricating composition, in particular a grease.

One or more of the above or other objects are obtained by the present invention by providing a lubricating composition, at least comprising:

-   -   a base oil;     -   a metal sulphide or metal oxide, preferably a metal sulphide;         and     -   an organosulphur compound.

Surprisingly, it has been found according to the present invention that lubricating compositions containing a metal sulphide or a metal oxide as well as an organosulphur compound exhibit an unexpected improvement in extreme pressure and anti-wear properties as measured by the four-ball test according to ASTM D2596.

An important advantage of the present invention is that improved extreme pressure properties may be obtained at the same total additive concentration, but also equivalent extreme pressure performance using lower concentrations of additives. This not only results in a reduction of costs (a smaller amount of relatively expensive additives is needed), but also avoids or reduces some of the problems associated with typical extreme pressure additive concentrations such as corrosion, oxidation instability, and reduced product life at high temperature.

There are no particular limitations regarding the metal sulphide or metal oxide used in the lubricating composition according to the present invention, and various conventional metal sulphides or metal oxides, alone or in combination, may be conveniently used. Examples of metal sulphides or metal oxides are Bi₂S₃, ZnS, WS₂, Sb₂S₃, MoS₂, Fe₂S₃, ZnO, TiO₂, MoO₃, etc.

According to a preferred embodiment of the present invention a metal sulphide is used (rather than a metal oxide), wherein the metal sulphide is preferably selected from the group consisting of Bi₂S₃, ZnS, WS₂ and MoS₂. It is even more preferred that the metal sulphide is Bi₂S₃.

The organosulphur compound can be selected from a broad range of compounds.

Preferably the organosulphur compound is a compound obtainable by sulphurisation of a compound containing unsaturated hydrocarbon moieties, the hydrocarbon moieties preferably containing only H and C atoms. Particularly preferred are sulphurised esters and fats and sulphurised polyalkenes (such as polybutenes).

Examples of suitable organosulphur compounds and the preparation thereof are disclosed in U.S. Pat. No. 4,191,659, the teaching of which is herein incorporated by reference.

Non-limiting examples of these organosulphur compounds may be obtained by sulphurising olefinic compounds (i.e. having at least one non-aromatic double bond), such as compounds having the general formula (1)

R¹R²C═CR³R⁴  (1)

wherein each of R¹, R², R³ and R⁴ is individually selected from hydrogen or an organic moiety.

In general, the organic moieties of R¹-R⁴ (if not hydrogen) may be groups as —C(R⁵)₃, —COOR⁵, —CON(R⁵)₂, —COON(R⁵)₄, —COOM, —CN, —C(═NR⁵)R⁵, —X, —YR⁵ or —Ar, wherein:

each R⁵ is independently hydrogen, alkyl, alkenyl, aryl, substituted alkyl, substituted alkenyl or substituted aryl, with the proviso that any two R⁵ groups can be alkylene or substituted alkylene whereby a ring of up to about 12 carbon atoms is formed;

M is one equivalent of a metal cation (preferably Group I or II, e.g., sodium, potassium, barium, calcium);

X is halogen (e.g., chloro, bromo, or iodo);

Y is oxygen or divalent sulphur;

Ar is an aryl or substituted aryl moiety of up to about 12 carbon atoms.

Any two of R¹-R⁴ may also together form an alkylene or substituted alkylene group; i.e., the olefinic compound may be alicyclic.

The natures of the substituents in the substituted moieties described above are not normally a critical aspect of the invention. Typical examples of such substituents include any of the above-listed moieties as well as hydroxy, amidine, amino, sulfonyl, sulfinyl, sulfonate, nitro, phosphate, phosphite, alkali metal mercapto and the like.

The olefinic compound is usually one in which each R value which is not hydrogen is independently alkyl, alkenyl or aryl, or (less often) a corresponding substituted radical. Mono-olefinic and diolefinic compounds, particularly the former, are preferred, and especially terminal mono-olefinic hydrocarbons; that is, those compounds in which R³ and R⁴ are hydrogen and R¹ and R² are alkyl or aryl, especially alkyl (that is, the olefin is aliphatic). Olefinic compounds having about 3-30 and especially about 3-16 (most often less than 9) carbon atoms are particularly desirable.

Isobutene, propylene and their dimers, trimers and tetramers, and mixtures thereof are especially preferred olefinic compounds. Of these compounds, isobutylene and diisobutylene are particularly desirable because of their availability and the particularly high sulphur-containing compositions which can be prepared therefrom.

For the preparation of the above non-limiting examples of organosulphur compounds, specific reference is again made to U.S. Pat. No. 4,191,659, the teaching of which is incorporated by reference. Examples of commercially available organosulphur compounds which can be suitably used according to the present invention are Roscan 144 available from PCAS (Longjumeau, France) and SVE 10C available from Harrison Manufacturing Company Ltd. (Australia).

According to a preferred embodiment of the present invention, the organosulphur compound has a S content in the range of from 5 to 40 wt. %, preferably from 7 to 20, more preferably from 8 to 12 wt. %, based on the weight of the organosulphur compound.

Further it is preferred that the lubricating composition has a S content in the range of from 0.1 to 10 wt. %, preferably from 1 to 8 wt. %, based on the finished lubricating composition.

According to an especially preferred embodiment of the present invention, the composition is in the form of a grease and contains one or more thickeners.

There are no particular limitations regarding the base oil composition used in the method according to the present invention, and various conventional mineral oils and synthetic oils may be conveniently used. For the purpose of this description, the term “base oil” is meant to also include a grease base stock.

The base oil composition used in the present invention may conveniently comprise mixtures of one or more mineral oils and/or one or more synthetic oils.

Mineral oils include liquid petroleum oils and solvent-treated or acid-treated mineral lubricating oil of the paraffinic, naphthenic, or mixed paraffinic/naphthenic type which may be further refined by hydrofinishing processes and/or dewaxing.

Suitable base oils for use in the lubricating oil composition of the present invention are Group I, Group II or Group III base oils, polyalphaolefins, Fischer-Tropsch derived base oils and mixtures thereof.

By “Group I” base oil, “Group II” base oil and “Group III” base oil in the present invention are meant lubricating oil base oils according to the definitions of American Petroleum Institute (API) categories I, II and III. Such API categories are defined in API Publication 1509, 15th Edition, Appendix E, April 2002.

Suitable Fischer-Tropsch derived base oils that may be conveniently used as the base oil in the lubricating oil composition of the present invention are those as for example disclosed in EP 0 776 959, EP 0 668 342, WO 97/21788, WO 00/15736, WO 00/14188, WO 00/14187, WO 00/14183, WO 00/14179, WO 00/08115, WO 99/41332, EP 1 029 029, WO 01/18156 and WO 01/57166.

Synthetic oils include hydrocarbon oils such as olefin oligomers (PAOs), dibasic acid esters, polyol esters, and dewaxed waxy raffinate. Synthetic hydrocarbon base oils sold by the Shell Group under the designation “XHVI” (trade mark) may be conveniently used.

The total amount of base oil incorporated in the lubricating composition of the present invention is preferably present in an amount in the range of from 60 to 99 wt. %, more preferably in an amount in the range of from 75 to 99 wt. % and most preferably in an amount in the range of from 75 to 98 wt. %, with respect to the total weight of the lubricating composition.

The total amount of the metal sulphide and/or metal oxide in the final lubricating composition is typically in the range of from 0.5 to 10.0 wt. %, preferably from 1.0 to 5.0 wt %, based on the total weight of the lubricating composition.

The total amount of the organosulphur compound oxide in the final lubricating composition is typically in the range of from 0.5 to 10.0 wt. %, preferably from 1.0 to 5.0 wt %, based on the total weight of the lubricating composition.

If desired, the final lubricating composition may further comprise one or more additives such as anti-oxidants, anti-wear agents, dispersants, detergents, friction modifiers, viscosity index improvers, pour point depressants, tackifying agents, corrosion inhibitors, demulsifiers, defoaming agents and seal compatibility agents, etc.

As the person skilled in the art is familiar with the above and other additives, these are not further discussed here.

Said additives are typically present in an amount in the range of from 0.01 to 12.5 wt. %, based on the total weight of the lubricating composition, preferably in an amount in the range of from 0.05 to 10.0 wt. %, more preferably from 1.0 to 9.0 wt. % and most preferably in the range of from 2.0 to 5.0 wt. %, based on the total weight of the lubricating composition.

As the lubricating composition may also be (and preferably is) in the form of a grease, the base oil as contained in the lubricating composition may contain or be compounded with one or more thickeners such as metallic soaps, organic substances or inorganic substances, for example, lithium soaps, lithium complex soaps, sodium terephthalate, urea/urethane compounds and clays.

Preferably, the lubricating composition has a kinematic viscosity at 100° C. (ASTM D445) in the range of from 2 to 80 mm²/s, more preferably in the range of from 3 to 70 mm²/s, most preferably in the range of from 4 to 50 mm²/s.

The lubricating compositions of the present invention may be conveniently prepared by admixing the one or more base oils and, optionally, one or more additives that are usually present in lubricating compositions, for example as herein before described, with mineral and/or synthetic base oil. Preferably, the metal sulphide(s) or metal oxide(s) used has (have) a sufficiently small particle size (e.g. below 50 μm, preferably below 20 μm) to allow easy dispersion thereof in the lubricating composition.

In another aspect the present invention provides a method for improving one or more of extreme pressure and anti-wear properties, which method comprises lubricating with a lubricating composition according to the invention. Also, the present invention provides the use of a lubricating composition according to the present invention for improving one or more of extreme pressure and anti-wear properties, in particular according to ASTM D2596.

The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the present invention in any way.

EXAMPLES Lubricating Oil Compositions

Table 1 indicates the composition of the lubricating oil compositions that were tested; the amounts of the components are given in wt. %, based on the total weight of the fully formulated formulations.

The “grease base stock” as used in Example 1 and Comparative Examples 1-4 was a conventional grease base stock and contained about 10% m/m lithium 12-hydroxystearate thickener and about 90% m/m paraffinic mineral base oil blended from SN 500 and bright stock (viscosity at 40° C. of 180 mm²/s according to ASTM D445).

“Bi₂S₃” is available from e.g. Miracema-Nuodex (Brazil).

The “organosulphur compound” as used in Example 1 is a sulphurised ester available from PCAS (Longjumeau, France) under the trade designation “Roscan 144”.

The compositions of Example 1 and Comparative Examples 2-4 were obtained by simply mixing the grease base stock, the Bi₂S₃ and the sulphurised ester, if present, using a laboratory paddle mixer.

TABLE 1 Component Example Comp. Comp. Comp. Comp. [wt. %] 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Grease base stock 92.0 100 97 92.0 92.0 Bi₂S₃ 3.0 — 3.0 8.0 — Sulphurised ester 5.0 — — — 8.0 TOTAL 100 100 100 100 100

Load Capacity Test

In order to demonstrate the extreme pressure and anti-wear properties of the lubricating compositions according to the present invention, measurements according to the standard test ASTM D2596 at various loads were performed. In line with the standard test, all tests were started at room temperature.

The measured wear scars (in mm) are indicated in Table 2 below. Table 2 also shows the load at which the respective compositions failed, which loads were maintained for 1 minute or until failure occurred within 1 minute. Failure occurs when the upper ball as used in the test becomes intimately bonded, or welded to, the three lower balls. This is signified by a significant increase in noise and vibration from the test equipment and is often accompanied by smoke emanating from the contact between the balls.

TABLE 2 Load Example Comp. Comp. Comp. Comp. [kg] 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 100 0.53 2.40 0.71 0.58 0.70 150 0.78 failed 0.88 0.78 1.60 250 1.86 1.76 1.38 2.00 400 2.15 failed failed failed 500 2.20 600 2.40 700 failed Weld load 800 150 400 400 315 [kg]

Discussion

As can be seen from the Examples, the lubricating composition according to the present invention provides an unexpected improvement in extreme pressure and anti-wear properties as measured according to ASTM D2596,

As can be seen from Comparative Examples 1-3, the presence of a typical concentration of 3 wt. % (Comparative Example 2) and a high concentration of 8 wt. % (Comparative Example 3) bismuth sulphide results in weld load of 400 kg, which is deemed to be a good weld load value for a grease for extreme pressure purposes. In this respect it is noted that by increasing the amount of bismuth sulphide from 3 to 8 wt. % no advantage in extreme pressure performance seems to be obtained; this suggest that 400 kg can be considered as a maximum value which can be achieved.

By using (a relatively high amount of) 8 wt. % sulphurised ester alone (Comparative Example 4) a weld load of 315 kg was achieved, showing a degree of extreme pressure performance when compared with Comparative Example 1 (containing no sulphurised ester).

Surprisingly, Example 1 according to the present invention (containing both sulphurised ester and bismuth sulphide) allows to achieve a weld load of well above 400 kg. The unexpectedly high weld load of 800 kg as achieved according to the present invention would be considered as a very high extreme pressure performance, suitable for greases in the highest loaded applications.

An important advantage of the present invention is that improved extreme pressure properties may be obtained at the same total additive concentration, but also equivalent extreme pressure performance using lower concentrations of additives. This not only results in a reduction of costs (a smaller amount of relatively expensive additives is needed), but also avoids or reduces some of the problems associated with typical extreme pressure additive concentrations such as corrosion, oxidation instability, and reduced product life at high temperature.

In addition to the benefits in carrying of high loads without failure as detailed above, the present invention shows also benefits in wear protection, as shown by the size of the wear scars shown above, from the tests which were run at loads less than the failure loads. For example, at a moderate load of 100 kg, which would be considered a typical load for a large proportion of standard applications, Example 1 according to the present invention shows the smallest wear scar size compared with all Comparative Examples. Equally at 150 kg, a somewhat higher but still moderate load, the wear scar size from the test with Example 1 was equal lowest, together with Comparative Example 3, containing a large amount of bismuth sulphide. Such a large amount of bismuth sulphide as in Comparative Example 3 would represent a very considerable raw material cost to the lubricant producer and would probably not be considered in industrial practice. 

1. A lubricating composition, comprising: a base oil; a metal sulphide or metal oxide; and an organosulphur compound.
 2. The lubricating composition according to claim 1, wherein the metal sulphide is selected from the group consisting of Bi₂S₃, ZnS, WS₂ and MoS₂.
 3. The lubricating composition according to claim 2, wherein the metal sulphide is Bi₂S₃.
 4. The lubricating composition according to claim 3, wherein the organosulphur compound is a compound obtainable by sulphurisation of a compound containing unsaturated hydrocarbon moieties, wherein the hydrocarbon moiety contains only H and C atoms.
 5. The lubricating composition according to claim 4, wherein the organosulphur compound has a S content in the range of from 5 to 40 wt. %, based on the weight of the organosulphur compound.
 6. The lubricating composition according to claim 5, wherein the lubricating composition has a S content in the range of from 0.1 to 10 wt. %, based on the finished lubricating composition.
 7. The lubricating composition according to claim 6, being in the form of a grease and containing one or more thickeners.
 8. (canceled) 